Vibration attenuation assembly with venting passageway

ABSTRACT

The present invention features a vibration attenuation assembly designed for the protection of single axis instruments such as accelerometers. The assembly includes an inner cylinder housing one or more single axis accelerometers co-aligned with a principle axis of the cylinder. The inner cylinder is suspended by three or more equally spaced springs at each end. The springs also function as electrical conductors for transmitting power and signals to the accelerometer. The inner cylinder is longitudinally shiftable within the outer cylinder and a main fluid cavity exists between the exterior surface of the inner cylinder and the inner surface of the outer cylinder. A rigid outer cap is provided at both ends of the outer cylinder and a rigid inner cap is provided at both ends of the inner cylinder. A damping fluid end cavity is provided between an end cap of the inner cylinder and an adjacent end cap of the outer cylinder and at least one longitudinally extending vent passageway, formed either on the inner or outer cylinder, opens into the damping fluid end cavity. The vent passageway or passageways extend the longitudinal length of the inner cylinder when they are integrally formed with the inner cylinder.

This is a division of co-pending U.S. application Ser. No. 07/597,717filed on Oct. 12, 1990, now U.S. Pat. No. 5,117,695.

FIELD OF THE INVENTION

An attenuation assembly which protects single axis precision instrumentssuch as single axis accelerometers by reducing the affects of externalvibrations or shocks on the instrument.

BACKGROUND DISCUSSION

High precision single axis accelerometers for use in monitoringacceleration changes in various environments have taken on specialimportance in areas such as in space microgravity experiments. Theability of such high precision accelerometers to detect minutegravitational changes makes it necessary to avoid subjecting the highprecision instruments to forces which could adversely influence theperformance of the instruments.

The use of fluid damping to prevent accelerometers from having undampedoscillatory dynamic response characteristics which can result ininaccurate measurements is known in the art. For example, U.S. Pat. Nos.3,813,946 and 4,159,502 discuss the use of fluid damping in associationwith precision instruments such as gyroscopes and accelerometers. Thedamping systems of 3,813,946 and 4,159,502 are not well suited forachieving the exacting damping functions required to ensure properreadings of the high precision instruments presently being used, forexample, in microgravity tests and low gravity manufacturing processes.

U.S. Pat. No. 4,019,389 illustrates a viscous damper for damping linearvibrations along an axis of a vibrating beam in an attempt to isolatethe instruments from the external vibrations. Again, however, theviscous damping arrangement of U.S. Pat. No. 4,019,389 is not wellsuited for achieving the exacting requirements for properly damping highprecision instruments.

SUMMARY OF THE INVENTION

The present invention features a vibration attenuation assembly which isdesigned to protect singal axis accelerometers or any other device whichis sensitive to vibration in a single direction when the device issubjected to high shock or vibration in all directions. The vibrationattenuation assembly of the present invention is especially suited forreducing high frequency vibration noise in accelerometers which canobscure more critical near constant acceleration inputs, in particular,frequencies as low as several Hz and as high as several hundred Hz. Thisis accomplished while retaining lateral stability, avoiding angularrotations about the two non principal axis, and avoiding reducedattenuation capabilities due to parasitic inertia. The vibrationattenuation device is thus well suited for use in high precisionaccelerometers placed in a low gravity (e.g. space) environment. Thedesign of the present invention is not limited to such an application,however, as the vibration attenuation assembly is also well suited forother environments.

A first embodiment of the present invention features an inner cylinder(or inner housing) within which one or more accelerometers (or otherprecision instruments) are mounted. The accelerometers are positionedsuch that the sensitive axis of the accelerometers is co-aligned withthe principal axis of the cylinder. The inner cylinder is heldessentially in a concentric, suspended relationship with respect to alarger outer cylinder (or outer housing). Suspension of the innercylinder within the outer cylinder is achieved through the use of threeof more equally spaced springs extending between the exterior of theinner cylinder and the interior of the outer cylinder at or near thecylinder's ends. The springs are arranged perpendicular to thecylinders' axis or at a slight angle to the perpendicular. Thisarrangement provides for greater longitudinal stiffness. In a preferredembodiment, three springs spaced at 120° intervals are provided at eachend of the double cylinder assembly.

A preferred manner of mounting the accelerometer(s) within the innercylinder is to provide the inner cylinder with an internal circularflange to which a plate of the accelerometer is secured by bolts or thelike.

To protect the accelerometer from adverse affects due to, for instance,air currents or floating debris, end caps are provided at the ends ofthe inner cylinder.

In an alternate embodiment of the present invention, there is provideddamping means between the inner and outer cylinders in combination withthe springs. One contemplated manner of achieving the damping of theradial springs involves providing a visco elastic coating on thesprings. The coating can be applied to the springs in a spraying ordipping process, preferably the coating is thin enough such that thecoils are free to expand or retract whereby the stiffness of the springsis maintained relatively low. A latex paint high in elastomeric contentwould be suitable for the proposes of this invention.

Another embodiment of the present invention features an eddy currentdamper assembly positioned at one or both ends of the double cylinderassembly. For this embodiment, the inner cylinder is shorter in lengththan the outer cylinder. Both the outer cylinder and inner cylinderinclude capped ends. Between the exterior of the capped inner end andthe interior of the capped outer end is positioned an eddy currentdamper assembly. In a preferred embodiment, one or, more preferably, aplurality of copper plates are fastened and extend outward from theinner cap. Extending from the interior surface of the outer cylinder'scap and fixed thereto are an equal number of coil structures which aredimensioned and arranged such that the plates are received therebetweenor therein. The inner cylinder is thus free to longitudinally andradially float to a limited extent within the coil structures of theouter cylinder. In a preferred embodiment three copper plates arrangedat 120° intervals extend out away from each inner cylinder end cap andare received within three coil structures extending inwardly off each ofthe outer cylinder's end caps.

The present invention further includes an embodiment wherein a dampingfluid is positioned between the exterior of the inner cylinder and theinterior of the outer cylinder. In addition to the fluid dampingmaterial the previously described springs can also be provided. Theinner cylinder can be made essentially the same length as that of theouter cylinder. Furthermore, no coverings or caps are provided at theends of the inner and other cylinder. Rather, the surface tension of thefluid and the adhesion of the fluid to the interior surface of the outercylinder and the exterior surface of the inner cylinder is relied uponto maintain the fluid in place. This embodiment has specialapplicability for in space use wherein the fluid would not as easily besubjected to high gravity forces which could result in fluid leakingpermanently out away from the cylinders. A distance between the innerand outer cylinder of about 0.030" to 0.050" or more preferably about0.040" is suitable for this embodiment when it is used in a low gravityspace environment. For all fluid damping embodiments, cross-axis dampingis provided by the squeeze film effect.

The damping fluid can be conventional machine oil, glycerol, silicone,or any other suitable damping fluid with the particular materialdepending upon the damping required, the contemplated use, the durationof use and environmental conditions.

Use of the uncovered or uncapped damping fluid would also be possiblefor ground testing, but would require a very thin cavity between theexterior of the inner cylinder and the interior of the outer cylinder toensure that no fluid leakage occurs. A cavity depth of about 0.008" to0.020" or, more preferably, about 0.015" is contemplated for use in thepresent invention.

Preferably, for the embodiment using uncapped fluid damping thecylinders are formed of an aluminum alloy which has a relatively poroussurface which provides high adhesion between the damping fluid and thecylinder. To prevent capillary action drawing the fluid out of thecylinders, a ring of essentially non-wetting material (e.g., teflon orplastic) is provided at each end of each cylinder.

For each of the previously described embodiments the spring members actas electrical conducts for providing electrical current to theaccelerometer and for receiving the signals from the accelerometer(s).This approach removes the additional stiffness that would be encounteredif lead wires were used. To protect against short circuiting, adielectric ring can be provided at each end.

An alternate embodiment of the invention is similar to that describedabove in that a damping fluid is provided between the exterior of theinner cylinder and the interior of the outer cylinder. The damping fluidis used in conjunction with the springs positioned between the twocylinders at the cylinder ends. Rather than relying on fluid surfaceadhesion to maintain the damping fluid in place, membranes are providedat each end of the double cylinder assembly. The membranes are used toseal the ends of the cavity formed between the exterior of the innercylinder and the interior of the outer cylinder. To prevent the flowingfluid's own inertia from altering the readings of the accelerometer asthe fluid travels longitudinally between the two ends of the doublecylinder assembly, the membrane at each end is formed of a soft elasticmaterial. A soft elastomeric material which is capable of a gradualextension and slow retraction would be well suited for the presentinvention. A synthetic or natural rubber latex such as that used forsurgical gloves is contemplated for use in present invention, althoughother materials having the above described characteristics could be usedin place of a latex material.

In another embodiment of the present invention, damping fluid ventpassageways in the form of longitudinally extending tubes are providedin either the inner cylinder or the outer cylinder to allow for pressurerelease of the damping fluid inserted between the inner and outercylinders. The embodiment features radial springs which are containedwithin radially extending chambers forming part of the outer cylinderand have their inner ends connected to the inner cylinder. A rigid outercap is provided at both ends of the outer cylinder and rigid inner capis provided at both ends of the inner cylinder. A lock screw can beprovided to lock the inner cap to the outer cap at one end of the doublecylinder arrangement. Thus, during periods where higher accelerationlevels are known to exist (e.g. space vehicle launches), the innercylinder and outer cylinder can be locked in position through use of thelocking screw. When, however, the accelerometer is to be placed in use,the lock screw can be retracted (not withdrawn) to a position where theinner cylinder is no longer locked in position but free to movelongitudinally within the outer cylinder.

The inner cylinder is provided with a plurality of the above mentionedventing tubes arranged along the inner cylinder's interior wall. Acavity is formed at the inner side of one of the exterior end caps suchthat intentionally trapped air in the end cavities is free to flowthrough the vent tubes to equalize pressure in each end cavity. Thequantity of damping fluid used is limited to that which will fill thespace between the cylinders by capillary action and that which willadhere as a thin film to the end cavity and vent tube walls so as not tointerfere with air flow from one end cavity to the other.

An additional embodiment of the invention positions fluid springs withinthe cavity between the exterior of the inner cylinder and the interiorof the outer cylinder. In a preferred embodiment, the fluid springs areconductive and are used in place of the non-fluid springs. The fluidsprings can be retained within wells formed in the interior surface ofthe outer cylinder or the exterior of the inner cylinder or both.

During periods wherein it is known that the double cylinder assemblywill be subjected to high accelerations or impact, a safety feature isprovided so as to avoid the dispersion of the fluid forming the fluidsprings. In a preferred embodiment, a lock screw is threaded through theouter cylinder. The lock screw has a concave end surface which forms anarea in contact with an upper portion of a fluid spring. By designingthe cavity in the lock screw and the complementary cavity formed in theexterior surface of the inner cylinder with a sufficient depth, it ispossible to screw the lock screw down completely so as to place a flangeof the lock screw in contact with the exterior of the inner cylinder.The contact of the flange with the exterior of the inner cylinder sealsthe fluid spring within a cavity defined by the concave end of the lockscrew and the well formed in the exterior of the inner cylinder. Whentesting is to be performed, the lock screw is retracted until the flangeat the end of the lock screw is received within a complementary recessformed in the inner surface of the outer cylinder.

The fluid springs can be used either alone or in combination withdamping fluid positioned between the exterior of the inner cylinder andthe interior of the outer cylinder. For example, an oil can be used inconjunction with mercury fluid springs contained in wells with the oileither retained by capillary action as discussed above or by addition ofmembranes such as those described above. The damping fluid chosen, ofcourse, must be compatible with the fluid springs.

Alternatively, the conductive fluid springs can be used together withnonconductive fluid springs of a different material. For example, byproviding a plurality of wells along the longitudinal length of thedouble cylinder arrangement there can be positioned conductive fluidsprings toward the ends together with nonconductive fluid springspositioned between the conductive fluid springs or between and to theoutside of the conductive fluid springs.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a perspective view of a first embodiment of the presentinvention;

FIG. 2 shows a cross sectional view taken along line II--II of FIG. 1;

FIG. 3 shows in cross section an alternate embodiment of the presentinvention;

FIG. 4 shows in greater detail one of the spring chambers shown in FIG.3;

FIG. 5 shows a cross sectional view of the dampened spring taken alongline V--V in FIG. 4;

FIG. 6 shows a longitudinally cross sectional view of an additionalembodiment of the present invention;

FIG. 6A shows in greater detail one end of the inner cylinder;

FIG. 7 shows in partially cut away view an alternate embodiment of thepresent invention;

FIG. 8 shows a longitudinal, cross-sectional view of an additionalembodiment of the present invention;

FIG. 9 shows a cross sectional view taken along cross section lineIX--IX found in FIG. 8.

FIG. 10 shows, in cut-away, a longitudinal, cross-sectional view of anadditional embodiment of the present invention taken along cross-sectionline X--X;

FIG. 11 shows an end view of the embodiment shown in FIG. 10 taken fromthe view point of line XI--XI in FIG. 10;

FIG. 12 shows in perspective an additional embodiment of the presentinvention which utilizes fluid springs;

FIG. 13 shows an end view of that which is shown in FIG. 12;

FIG. 14 shows in a cut-away view a portion of that which is shown inFIG. 12;

FIG. 15 illustrates a lock screw positioned over the fluid springs shownin FIG. 14;

FIG. 16 shows in a cut-away view an alternate embodiment of theinvention utilizing fluid springs in combination with secondary fluiddamping material; and

FIG. 17 shows an additional embodiment of the present invention whichpositions secondary fluid springs along and the adjacent to the primaryfluid springs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a perspective view of a first embodiment of the presentinvention which comprises a vibration attenuation assembly 30 designedto protect single axis instruments such as an accelerometer. Vibrationattenuation assembly 30 includes outer cylinder 32 (or housing) with aplurality of spring chambers 34 extending radially thereoff. Springchambers 34 house springs 36 which have a first end connected to theouter end of spring chamber 34 and a second end connected to innercylinder 38. In a preferred embodiment, inner cylinder 38 is suspendedby three or more equally spaced springs at each end. Preferably, eachspring is attached perpendicular to the cylinder axis or, alternativelyat a slight angle to the perpendicular inward for greater longitudinalstiffness. For the purposes of this invention, a suitable spring isspring number C0057-006-0620 of Associated Raymond Springs Co. FIG. 1further illustrates support 40 supporting assembly 30 and attacheddirectly to a fixed surface or, alternatively, attached indirectly (anadditional spring or damping assembly) to a fixed structure.

FIG. 2 illustrates a cross sectional view take along cross section lineII--II in FIG. 1 with the support structure 40 removed from view. Asshown in FIG. 2, spring chambers 34 are attached to the exterior ofouter cylinder 32 and are positioned essentially at an equal angle fromone another (e.g., 120°). FIG. 2 further illustrates accelerometer 42positioned so as to have its sensitive axis co-aligned with theprinciple axis of the inner cylinder 38. In a preferred embodiment,accelerometer 42 is fixed in place by accelerometer support bracket 44which, in this embodiment, features three radially extending armsextending outwardly to flange 46.

Flange 46 is formed along the interior of inner cylinder 38 and includesa plurality of threaded holes for receipt of threaded connection memberswhich pass through each leg of accelerometer support member 44. Radialsprings 36 suspend inner cylinder 38 with respect to outer cylinder 32to form cavity 48. In addition to suspending the inner cylinder andacting as a compressible spring, radial springs 36, even when completelyperpendicular to the longitudinal axis, act as a weak longitudinalspring while acting as a stiff lateral spring. The weak or softlongitudinal spring movement is helpful in obtaining a low, longitudinalnatural frequency in the system. Lateral stiffness provides a way toreduce coneing and other error producing dynamics.

Radial springs 36 can also function as electrical conductors for theintroduction of power and for allowing the passage of signals to andfrom the accelerometer or accelerometers positioned within the innercylinder. The radial spring arrangement provides near linear springresponse for small longitudinal displacement which is desirable forachieving nondistorted signals from the accelerometer. Radial springs36, upon being subject to a high impact, will stretch in accordance withtheir spring constant as well as deflect longitudinally such that largerdisplacements result in larger than proportional nonlinear response. Thenonlinearly response of the radial springs 36 thus provides protectionfrom end impact of the displaceable member inside the accelerometer.Furthermore, the longitudinal softness of the springs and slightlongitudinal distortion of the springs, upon forces being applied alongthe sensitive axis of the accelerometer, have been found not to generatea persistent hysteresis which would be detrimental to testing,calibrating or utilizing an accelerometer.

FIG. 3 illustrates a cross sectional view taken through the springchamber 34 of an alternate embodiment of the present invention. Tosimplify the illustration, the accelerometer and accelerometer'smounting bracket have been removed from the view. FIG. 3 illustrates anembodiment which is similar to that shown in FIG. 2 with the exceptionthat radial springs 36 found in the embodiment of FIG. 2 have beenmodified to include damping means. Accordingly, modified radial springs36' (FIG. 3) provide both a spring function and a damping function asinner cylinder 38 moves longitudinally and radially with respect toouter cylinder 32.

FIG. 4 shows in greater detail one of the spring chambers 34 shown inFIG. 3. As shown in FIG. 4, spring chamber 34 includes electricalconnector 50 from which wire or wires 52 extend. Spring chamber 34 alsoincludes a spring receiving means 54 which receives one end of modifiedradial spring 36'. Spring receiving means 54 is formed of a dielectricmaterial such as a ceramic or epoxy so as to insulate the spring fromcontact with chamber 34. As shown in FIG. 3, an insulating block 55 isprovided at the other end to insulate the spring from contact with innercylinder 38. Wire 52 extends to the accelerometer from the end of spring36'.

FIG. 5 illustrates a cross sectional view of spring 36' taken alongcross section line V--V of FIG. 4. Modified spring 36' is comprised ofspring member 56 having its exterior coating with covering 58. Covering58 is preferably formed of a visco elastic material such as anelastomeric paint (e.g., latex paint with elastomeric components). Thethickness of the covering 58 can be varied in accordance with theanticipated environment which modified springs 36' will be used.However, too thick a covering can cause excess rigidity especially whenthe covering of one section of spring member 56 becomes integral withthe covering of an over lying section of spring member 56. Preferably,the covering 58 is applied in a spraying process.

FIG. 6 shows an alternate embodiment of the present invention havingparticular applicability to a low gravity environment such as thosefound in space. The general arrangement shown in FIG. 6 is similar tothat which is shown in perspective in FIG. 1. FIG. 6 shows a crosssectional longitudinal view of the vibration attenuation assembly 60having a plurality of spring chambers 62. Cavity 64 which lies betweenthe interior of outer cylinder 66 and the exterior of inner cylinder 68forms a capillary ring within which damping fluid is provided. Thedamping fluid provided within cavity 64 relies on surface tension toachieve a damping function and to avoid leakage of the damping fluid.Accordingly, cavity 64 has a depth of about 0.030" to 0.050", or morepreferably, about 0.040". In other words, the fluid layer within cavity64 has an average thickness of about 0.030" to 0.050" or more preferablyabout 0.040".

Springs 36 as in FIG. 1 provide an electrical connection for passingcurrent to and from accelerometer 70. Accelerometer 70 is retained onaccelerometer bracket 72 and flange 74. To provide sufficient surfaceadhesion between the exterior of the inner cylinder and the interior ofthe outer cylinder, those surfaces of the cylinders are formed of arelatively porous material. For example, an unfinished or unpolishedaluminum alloy would be suitable for the purposes of the presentinvention.

FIGS. 6 and 6A illustrate the use of non-wetting rings 76 and 78provided at opposite ends of inner cylinder 68 and/or outer cylinder 62.As shown in FIG. 6A, non-wetting ring 78 can be inserted within aslotted recess formed in the interior 80 of inner cylinder 68.Non-wetting rings 76 and 78 provide a function of decreasing the surfaceadhesion between the fluid and the interior 80 so as to reduce thetendency for the damping fluid to be drawn out and away from the ends ofvibration attenuation assembly 62 in a capillary process. Thus,non-wetting rings 76 and 78 are formed of a material having a smoothexterior surface such as teflon, a dense plastic or a finely polishedmetal.

As mentioned above, the embodiment illustrated in FIG. 6 is specificallysuited for use in low gravity environments such as on a space vehicle.For use in an environment subject to higher gravitational forces such ason the surface of the earth, the non-covered cavity 64 can be utilizedbut would have to be of a depth which is about 0.020" or lower.

FIG. 7 shows an alternate embodiment of the present invention which issimilar to that described for FIG. 6 in that a fluid damping cavity 82is provided between the exterior of inner cylinder 84 and the interiorof outer cylinder 86. Again, inner cylinder 84 would be suspended fromouter cylinder 86 by way of a plurality of spaced radial springs 88contained within corresponding spring chambers 90. The embodiment ofFIG. 7, however, adds diaphragms 92 and 94 to cover the open ends ofcavity 82. Diaphragms 92 and 94 can be joined to the interior orexterior of cylinders 84 and 86 by any appropriate means such asadhesion with or without mechanical fasteners. As the membrane materialmust comply with cylinder motion, it must be made of a material havinglongitudinal material softness. In other words, diaphragms 92 and 94must expand and retract in a manner which avoids the development ofadditional spring forces. One embodiment of the present inventionutilizes a diaphragm formed of a natural or synthetic elastomeric latexmaterial.

FIG. 8 illustrates an alternate embodiment of the present inventionwhich utilizes both capillary action of a fluid and the longitudinalsoftness of radially extending springs to achieve a damping function ofthe movement of inner cylinder 96 with respect to outer cylinder 98. Asin the previous described embodiments, radial springs 100 are retainedwithin spring chambers 102 and are in electrical communication withelectric plug assembly 104. Accelerometer 106 is secured within theinterior of inner cylinder 96 and includes board 108 upon which can beinserted chips or similar electrical devices.

At one end of outer cylinder 98 is positioned, in fixed fashion, outercylinder end cap 110. At that same end, inner cylinder 96 includes innercylinder end cap 112. Inner cylinder end cap 112 is fixed in positionwith respect to outer cylinder end cap 110 by use of lock screw 114.Lock screw 114 extends through a threaded hole in end cap 110 and isdimensioned so as to be received within a threaded hole formed withininner cylinder end cap 112. This locking arrangement between outercylinder end cap 110 and inner cylinder end cap 112 provides a safetyfactor to avoid damage to the vibration attenuation assembly or theaccelerometer due to large impact or gravitational forces. For example,if the present invention is to be positioned within a vehicle to belaunched in space, during the launching high gravitational forces arecreated. Thus, lock screw 114 would be inserted within end cap 110 so asto prevent damage to the present invention due to the inner cylindershifting too far within outer cylinder 98.

FIG. 8 further illustrates another embodiment of the invention having amain damping fluid cavity 118 positioned between the interior of outercylinder 98 and the exterior of inner cylinder 96. Main damping fluidcavity 118 opens into damping fluid end cavity 116. Extendinglongitudinally and opening into damping fluid end cavity 116 are aplurality of venting passageways 120 which, as shown in FIG. 9, arespaced circumferentially about inner cylinder 96. The present inventionalso contemplates positioning vent passageways 120 on the interior ofouter cylinder 98 rather than the position shown in FIG. 9.

When lock screw 114 is retracted (but not completely withdrawn), innercylinder end cap 112 will be detached from outer cylinder end cap 110such that inner cylinder 96 will be free to shift longitudinally withrespect to outer cylinder 98. To dampen the shifting movement of innercylinder 96 with respect to outer cylinder 98, a damping fluid such asglycerol, silicon or motor oil is spaced within main damping fluidcavity 118, damping fluid end cavity 116, and, at least partially,within vent passage way 120.

With the damping fluid partially filling one end of vent passage way120, there is provided a means to compensate for the pressuredifferentials which arise when inner cylinder 96 shifts within outercylinder 98. In addition, both the surfaces defining the main dampingfluid cavity 118 and the venting passageway 120 are relatively poroussuch that the adhesion between the fluid and the porous surfacesprovides an added degree of damping. Moreover, as the embodiment shownin FIG. 8 is essentially a sealed system there is avoided the problemsassociated with damping fluid leakage and thus the embodiment has equalapplicability both in high gravitation environments and low gravitationenvironment.

FIGS. 10 and 11 illustrate still another embodiment of the presentinvention. As shown in FIG. 10, inner cylinder 122 extendslongitudinally within outer cylinder 124 and a clearance 126 ismaintained between the exterior surface of inner cylinder 122 and theinterior surface of outer cylinder 124. Inner cylinder 122 includes endcap 128 and mounting disk 130 positioned at the center and external endcap 128. Extending radially off mounting disk 130 are a plurality ofconducting plates 132 which are preferably arranged to extend radiallyout from a longitudinal center line as well as longitudinally out awayfrom mounting disk 130. Plates 132 extend between or within coilstructures 134 which maintain plates 132 in floating condition andprovide a damping function to plates 132 as plate 132 movelongitudinally within coil structure 134. The eddy current dampingassembly designated 136 can be provided at both ends of inner cylinder122 or only at one end. The eddy current damper option has the advantageof providing translational damping in all directions.

FIGS. 12-15 illustrate further embodiments of the present invention. Theembodiments illustrated in FIGS. 12 through 15 feature an alternatespring system which includes fluid springs 138. The fluid springs areformed of a fluid which has a high surface tension, low wettingpotential and also is conductive such that the fluid springs cancomplete an electrical circuit in a similar manner as radial springs 36.A suitable material for the fluid springs of this invention includesmercury. As shown in FIGS. 13-15, fluid springs 138 are retained inwells formed in both inner cylinder 140 and outer cylinder 142. As shownin FIG. 14, filling conduit 144 can be provided for allowing the initialfilling of the fluid spring or the replacement of a fluid springdislocated due to exposure to a high acceleration.

FIG. 15 illustrates an alternate manner of providing a fluid conduit 144for the positioning of fluid spring 138. Fluid conduit 144 in FIG. 15 isplugged by plug 146 which has threaded main body 148. Threaded main body148 includes a flanged end portion 150 as well as concave end 152partially defining the fluid spring well. The embodiment in FIG. 15,provides a safety feature to avoid dislocation of fluid springs 138 whenhigh acceleration forces are anticipated. For example, upon lift off ofa space vehicle, fluid spring 138, depending on the surface adhesion andthe depth of the wells, could possibly become dislocated. By threadingplug 146 until flange 150 contacts the exterior surface of innercylinder 140, fluid 138 can be essentially sealed from leakage out ofthe well. When the accelerometer is to be put to use, plug 146 isretracted to the position shown in FIG. 15 such that fluid spring 138can perform its damping and spring function.

Each fluid spring 138 can be electrically insulated from outer cylinder142 and electrically connected to a terminal 154 (FIG. 14) for thefeeding through of electrical power and signals. With the use of anelectrically conductive spring fluid, each fluid spring can then be usedas an insulated electrical path. Fluid spring 138 can be used alone orin combination with the previous described damping systems.

FIG. 16 illustrates fluid spring 138 retained between inner cylinder 140and outer cylinder 142 in a manner similar to that shown in FIG. 14.FIG. 16 also illustrates the additional use of secondary damping fluid156 positioned between the interior surface of outer cylinder 142 andthe exterior surface of inner cylinder 140. Again, capillary action canbe relied upon to maintain the secondary damping fluid in positionwithin cavity 156. Alternatively, the use of membranes as discussedabove can be relied upon. The secondary damping fluid has the advantageof providing a low thermal resistance path for cooling of theaccelerometer.

FIG. 17 illustrates yet another embodiment of the present inventionwherein, rather than relying upon secondary damping fluid 156,additional (nonconductive) fluid springs are arranged serially along thelongitudinal length of cavity 156. The damping fluid and fluid springsalso offer the advantage of a low thermal resistance path for theelimination of heat from the enclosed accelerometer.

Although the present invention has been described with reference topreferred embodiments, the invention is not limited to the detailsthereof. Various substitution and modifications will occur to those ofordinary skill in the art and such substitution and modifications areintended to fall within the spirit and scope of the invention as definedin the dependent claims.

What is claimed is:
 1. A vibration attenuation assembly, comprising anouter housing having a first end, a second end, and an interior surfacedefining a hollow interior;an inner housing having a first end, a secondend, an exterior surface, and a hollow interior, said inner housingbeing positioned within the hollow interior of said outer housing; amain damping fluid cavity positioned between the exterior surface ofsaid inner housing and the interior surface of said outer housing; and adamping fluid venting passageway in fluid communication with said maindamping fluid cavity.
 2. A vibration attenuation assembly as recited inclaim 1 further comprising a plurality of damping fluid ventingpassageways with each venting passageway comprising a tube extendingessentially longitudinally and forming an integral portion of said innerhousing.
 3. A vibration attenuation assembly as recited in claim 1further comprising a first and a second outer end cap attached torespective ends of said outer housing and a first and a second inner endcap attached to respective ends of said inner housing; and an enddamping fluid cavity being provided between said first outer end cap andsaid first inner end cap, and said end damping fluid cavity being influid communication with said damping fluid venting passageway and saidmain damping fluid cavity.
 4. A vibration attenuation assembly asrecited in claim 3 further comprising locking means for locking saidfirst outer end cap to said first inner end cap.
 5. A vibrationattenuation assembly as recited in claim 4 wherein said locking meansincludes a threaded member extending through said first outer end cap,and said first inner end cap having a threaded hole and said threadedmember being dimensioned and arranged so as to extend into and out ofthe threaded hole.
 6. A vibration attenuation assembly as recited inclaim 1 further comprising a plurality of radial springs positioned ateach end of said inner and outer housings, said radial springs extendingfrom said outer housing to the exterior surface of said inner housing soas to suspend said inner housing with respect to said outer housing, andsaid springs being substantially perpendicular with respect to alongitudinal axis of said inner housing.
 7. A vibration attenuationassembly as recited in claim 1 wherein said inner housing has alongitudinal length less than that of said outer housing such that saidinner housing is adapted for longitudinal displacement with respect tosaid outer housing.
 8. A vibration attenuation assembly as recited inclaim 1 wherein said fluid venting passageway includes a tube extendingessentially longitudinally and forming an integral portion of said innerhousing.
 9. A vibration attenuation assembly, comprising:a first housinghaving a first capped end, a second capped end, an exterior surface andan interior surface, and said interior surface defining a first interiorhollow; a second housing having a first capped end, a second capped end,an exterior surface and an interior surface, said second housing beingpositioned within the interior hollow of said first housing; springmeans connected with said first and second housing such that theexterior surface of said second housing is spaced from the interiorsurface of said first housing so as to define a main fluid cavitytherebetween, and the capped ends of said first and second housingsbeing spaced such that said second housing is free to move with respectto said first housing, said capped ends being dimensioned and arrangedsuch that a fluid end cavity is provided between a first pair ofadjacent capped ends, and one of said housings including a ventpassageway which extends from one end of said second housing to theother and opens into said fluid end cavity, and said main fluid cavitybeing in fluid communication with said fluid end cavity.
 10. A vibrationattenuation assembly as recited in claim 9 further comprising dampingfluid positioned within said main fluid cavity and adapted to flow intosaid fluid end cavity and a volume of gas positioned within said fluidend cavity and adapted for movement within said vent passageway upondamping fluid entering said end cavity.
 11. A vibration attenuationassembly as recited in claim 10 wherein a quantity of damping fluid isprovided in said assembly and the quantity of damping fluid is limitedto that which will fill the main fluid cavity and that which will adhereas a film within the end cavity and vent passageway so as not tointerfere with gas flow from one open end of the vent passageway to anopposite open end of the vent passageway.
 12. A vibration attenuationassembly as recited in claim 9 further comprising releasable lockingmeans for locking one capped end of said first housing to an adjacentcapped end of said second housing for preventing excessive movementbetween the first and second housings during periods of excessiveaccelerations.
 13. A vibration attenuation assembly as recited in claim12 wherein said releasable locking means includes a locking screw andthreaded reception areas in said adjacent capped ends.
 14. A vibrationattenuation assembly as recited in claim 9 wherein a plurality ofsprings are provided at opposite ends of said first and second housings.15. A vibration attenuation assembly as recited in claim 14 whereinthree metal coil springs are provided at each end of said housings andare peripherally equally spaced about each end of said housings.
 16. Avibration attenuation assembly as recited in claim 14 wherein saidsprings are electrically conductive and said housings include dielectricplugs so as to insulate said housings from said springs.
 17. A vibrationattenuation assembly as recited in claim 16 wherein said housings arecylindrical in shape and said first housing includes a plurality ofspring chambers extending radially out away from the inner surface ofsaid first housing.
 18. A vibration attenuation assembly as recited inclaim 9 wherein said vibration attenuation assembly includes a pluralityof vent passageways extending to opposite ends of said second housing.19. A vibration attenuation assembly as recited in claim 18 wherein saidplurality of vent passageways includes three vent passagewaysperipherally spaced about the interior surface of said second housing.